درس مهندسي نيازمندي ها استاد دكتر عبداله زاده دانشجو خيرالنسا مرچانت Requirement Engineering :A Roadmap

Introduction Software systems requirements engineering is the process of discovering the purpose by identifying stakeholders and their needs, and documents them in a form that is amenable to analysis communication and subsequent implementation. This paper describes the core Re activities: Eliciting requirements Modeling and analysis requirements Communicating requirements Agreeing requirements Evolving requirements

What is RE? The primary measure of success of a software system is the degree to which it meets the purpose for which it was intended software systems requirements engineering (RE) is the process of discovering that purpose identifying stakeholders their needs documenting these amenable to analysis communication subsequent implementation

RE difficulties Stakeholders may be numerous and distributed Their goals may vary and conflict, depending on their perspectives of the environment in which they work and the tasks they wish to accomplish Their goals may not be explicit or may be difficult to articulate satisfaction of these goals may be constrained by a variety of factors outside their control

Core RE activities eliciting requirements modeling and analyzing requirements communicating requirements agreeing requirements evolving requirements

Role of RE Requirements engineering is the branch of software engineering concerned with : the real-world goals for, functions of, and constraints on software systems. It is also concerned with the relationship of these factors to precise specifications of software behavior and to their evolution over time and across software families

Formalism Since software is a formal description, analysis of its behavior is amenable to formal reasoning Logic provides a vehicle for performing such analysis improve the rigor of the analysis performed to make the reasoning steps explicit

Formalism (Cont.) RE must span the gap between the informal world of stakeholder needs, and the formal world of software behavior the key question over the use of formal methods is not whether to formalize, but when to formalize

Context of RE The context in which RE takes place is usually a human activity system RE needs to be sensitive to how people perceive and understand the world around them how they interact how the sociology of the workplace affects their actions

Eliciting Requirements activity most often regarded as the first step in the RE process requirements are not out there to be collected simply by asking the right questions Information gathered during requirements elicitation often has to be interpreted analyzed modeled validated

Eliciting Requirements (Cont.) One of the most important goals of elicitation is to find out what problem needs to be solved, and hence identify system boundaries Identifying and agreeing a system's boundaries affects identification of Stakeholders user classes goals tasks scenarios use cases

Elicitation Techniques The choice of elicitation technique depends on the time and resources available to the requirements engineer the kind of information that needs to be elicited Some classes of elicitation techniques Traditional techniques Group elicitation techniques Prototyping Model-driven techniques Cognitive techniques Contextual techniques

Traditional techniques questionnaires surveys interviews analysis of existing documentation organizational charts process models standards user or other manuals of existing systems

Group elicitation techniques aim to foster stakeholder agreement brainstorming RAD/JAD workshops

Prototyping used for elicitation where there is a great deal of uncertainty about the requirements or where early feedback from stakeholders is needed

Model-driven techniques provide a specific model of the type of information to be gathered goal-based methods scenario-based methods

Cognitive techniques a series of techniques originally developed for knowledge acquisition for knowledge-based systems protocol analysis expert thinks aloud while performing a task, to provide the observer with insights into the cognitive processes used to perform the task Laddering using probes to elicit structure and content of stakeholder knowledge card sorting asking stakeholders to sort cards in groups, each of which has name of some domain entity repertory grids constructing an attribute matrix for entities

Contextual techniques emerged in the 1990's as an alternative to both traditional and cognitive techniques ethnographic techniques ethnomethodogy and conversation analysis

Elicitation Process With a plethora of elicitation techniques available to the requirements engineer, some guidance on their use is needed Elicitation techniques should be selected regarding particular application domain

Modeling and Analyzing Requirements Modeling - the construction of abstract descriptions that are amenable to interpretation - is a fundamental activity in RE The key question to ask for any modeling approach is "what is it good for?“ Categories of RE modeling Enterprise Modeling Data Modeling Behavioral Modeling Domain Modeling Modeling Nonfunctional Requirements Analyzing Requirements Models

Communicating Requirements RE is not only a process of discovering and specifying requirements, it is also a process of facilitating effective communication of these requirements among different stakeholders The focus of requirements documentation research is often on specification languages and notations the ability, not only to write requirements but also to do so in a form that is readable and traceable by many

Communicating Requirements (Cont.) Requirements traceability (RT) is another major factor that determines how easy it is to read Navigate Query Change requirements documentation Gotel defines requirements traceability as the ability to describe and follow the life of a requirement in both forwards and backwards direction

Agreeing Requirements As requirements are elicited and modeled, maintaining agreement with all stakeholders can be a problem especially where stakeholders have divergent goals Requirements validation is difficult for two reasons Philosophical what is knowable? Social difficulty of reaching agreement among different stakeholders with conflicting goals

Agreeing Requirements (Cont.) Jackson argues that descriptions used in RE should be refutable those that are not refutable are vague, and should only be treated as rough sketches win-win approach win conditions for each stakeholder are identified software process is managed and measured to ensure that all the win conditions are satisfied, through negotiation among the stakeholders

Evolving Requirements Managing change is a fundamental activity in RE because: Successful software systems always evolve as the environment in which these systems operate changes and stakeholder requirements change Changes to requirements documentation need to be managed. this involves providing techniques and tools for configuration management version control exploiting traceability links to monitor and control the impact of changes in different parts of the documentation

Evolving Requirements (Cont.) Traceability links does not support automated reasoning The links carry little semantic information ViewPoints framework address this problem In ViewPoints relationships between chunks of a specification are expressed operationally automated support for propagation of change becomes possible

Evolving Requirements (Cont.) Managing changing requirements is not only a process of managing documentation, it is also a process of: Recognizing change through continued requirements elicitation Reevaluation of risk evaluation of systems in their operational environment Nowadays one of the key research issues in software engineering is identifying core requirements in order to develop architectures that are: stable in the presence of change flexible enough to be customized and adapted to changing requirements

RE during the last decade The 1990's saw several important and radical shifts in the understanding of RE By the early 1990's, RE had emerged as a field of study in its own right, as witnessed by the emergence of two series of international meetings IEEE Springer By the late 1990's, the field had grown enough to support a large number of additional smaller meetings and workshops in various countries

RE during the last decade (Cont.) Three radical new ideas modeling and analysis cannot be performed adequately in isolation from the organizational and social context The notion that RE should not focus on specifying the functionality of a new system, but instead should concentrate on modeling indicative and optative properties of the environment RE has to take seriously the need to analyze and resolve conflicting requirements

Future Challenges Development of new techniques for formally modeling and analyzing properties of the environment, as opposed to the behavior of the software Bridging the gap between requirements elicitation approaches based on contextual enquiry and more formal specification and analysis techniques Richer models for capturing and analyzing non-functional requirements

Future Challenges (Cont.) Better understanding of the impact of software architectural choices on the prioritization and evolution of requirements Reuse of requirements models Multidisciplinary training for requirements practitioners

Reference Bashar Nuseibeh , Steve Easterbrook, Requirements engineering: a roadmap, Proceedings of the Conference on The Future of Software Engineering, p.35-46, Limerick, Ireland, June 4-11,2000.